It is known to use a vacuum bag apparatus to ensure good bonding between various laminates in a laminated structure during curing of the bonding material. These air bag apparatuses comprise a flexible membrane connected to a source of vacuum supply. For large size laminates, it has been found that the internal vacuum is not uniformly distributed over the entire surface of the laminates, resulting in poor bonding and/or air pockets remaining between the bonded laminates. This problem arises more particularly when making truck bodies out of a rigid substrate, like plywood, foam plastic or the like, and covered with a fiber-reinforced plastic material.